FQDNLookup failure could provide more information for diagnosing

[flyn-org]

• Version of collectd: 5.12.0
• Operating system / distribution: Alpine
• Kernel version (if applicable): N/a

Under some circumstances, collectd fails with the following error:

Looking up "[HOSTNAME]" failed. You have set the "FQDNLookup" option, but I cannot resolve my hostname to a fully qualified domain name. Please fix the network configuration.

This error message could be improved by the user of gai_strerror or, if the return code is EAI_SYSTEM, perror. As it stands the error message provides only limited information about what caused the error. This makes it a little more difficult to diagnose.

The relevant code is in src/daemon/collectd.c:

  char hostname[hostname_len];

  if (gethostname(hostname, hostname_len) != 0) {
    fprintf(stderr, "`gethostname' failed and no "
                    "hostname was configured.\n");
    return -1;
  }

  hostname_set(hostname);

  str = global_option_get("FQDNLookup");
  if (IS_FALSE(str))
    return 0;

  struct addrinfo *ai_list;
  struct addrinfo ai_hints = {.ai_flags = AI_CANONNAME};

  int status = getaddrinfo(hostname, NULL, &ai_hints, &ai_list);
  if (status != 0) {
    ERROR("Looking up \"%s\" failed. You have set the "
          "\"FQDNLookup\" option, but I cannot resolve "
          "my hostname to a fully qualified domain "
          "name. Please fix the network "
          "configuration.",
          hostname);
    return -1;
  }

[flyn-org]

See also https://gitlab.alpinelinux.org/alpine/aports/-/issues/15608.